Power transmission apparatus for hybrid electric vehicle

ABSTRACT

A power transmission apparatus for a hybrid electric vehicle having engine and motor may include: an input shaft coaxially disposed with an engine output shaft receiving engine torque; first and second output shafts disposed forward and rearward sides of the input shaft; a third output shaft coaxially disposed with the first output shaft; a shared drum connected to the input shaft and formed with a motor gear gear-meshed with the motor; an engine clutch arranged on the interior circumference of the shared drum and selectively transmitting torque between the engine output shaft and the input shaft; first and third clutches disposed within the shared drum and selectively transmitting torque from the input shaft to the first and third output shafts; and a second clutch disposed at a rearward side of the input shaft and selectively connecting the input shaft and the second output shaft.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 10-2019-0090444, filed on Jul. 25, 2019, the entirecontents of which are incorporated herein by reference.

FIELD

The present disclosure relates to a power transmission apparatus for ahybrid electric vehicle.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

Environment-friendly technology in vehicles is a core technology of afuture automobile industry, and automakers are focusing on developingenvironment-friendly vehicles to achieve environmental and fuelefficiency regulations.

In order to improve energy efficiency and driving convenience, varioustypes of vehicles have been developed, such as an electric vehicle (EV)and a hybrid electric vehicle (HEV) that utilize electrical energy, anda vehicle equipped with a double clutch transmission (DCT).

The hybrid electric vehicle is a vehicle using two or more power sourcesthat may be combined in various schemes. In general, a motor/generatordriven by electric energy is combined with either a gasoline or a dieselengine, which uses fossil fuels.

The DCT alternatingly activates odd-numbered shift-stages andeven-numbered shift-stages by alternatingly operating two clutches, andthereby improves continuity in torque transmission.

Recently, such a DCT is applied to a hybrid electric vehicle (HEV) so asto enhance an energy efficiency by reducing fuel consumption.

We have discovered that the efficient combination of the double clutchtransmission (DCT) and the hybrid electric vehicle (HEV), such asmodularizing the double clutch together with the motor of the hybridelectric vehicle, contributes to enhancing energy efficiency.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the present disclosureand therefore it may contain information that does not form the priorart that is already known to a person of ordinary skill in the art.

SUMMARY

The present disclosure provides a power transmission apparatus for ahybrid electric vehicle having advantages of reduced number of parts anddecreased length and weight by disposing two clutches in two rows in theradial direction to share a clutch drum at a forward portion of an inputshaft receiving a torque of the engine output shaft through an engineclutch, and separately disposing another clutch at a rearward portion ofthe input shaft.

Number of parts for receiving a torque of a motor may also be reduced bya power transmission apparatus for a hybrid electric vehicle where thetwo clutches disposed in two rows share a clutch drum with the engineclutch, and the clutch drum is formed with a motor gear externallygear-meshed with the motor to receive a torque from the motor.

When a clutch is separated to the rearward portion of the input shaft,there may be provided a better space at a forward portion of thetransmission for a differential gear, which provides an advantage in thelayout of the transmission.

In one form of the present disclosure, a power transmission apparatus,for a hybrid electric vehicle having an engine and a motor as powersources, may include: an engine output shaft, an input shaft, first andsecond output shafts, a third output shaft, a shared clutch drum, anengine clutch, first and third clutches, and a second clutch. The engineoutput shaft may receive a torque of the engine. The input shaft may becoaxially disposed with the engine output shaft. The first and secondoutput shafts may be formed as hollow shafts coaxial with the inputshaft, and respectively disposed at forward and rearward sides of theinput shaft without rotational interference. The third output shaft maybe formed as a hollow shaft and coaxially disposed with the first outputshaft without rotational interference.

The shared clutch drum may be disposed at a forward side of the inputshaft, and has a motor gear formed on an exterior circumference of theshared clutch drum to be externally gear-meshed with the motor. Theshared clutch drum may have an interior circumference rotatablysupported by a supporting end formed at a radially interior side of afront cover, and is connected to the input shaft through a connectionplate and a first connecting member. The engine clutch may be arrangedon the interior circumference of the shared clutch drum and beconfigured to selectively transmit a torque between the engine outputshaft and the input shaft. The first and third clutches may be disposed,adjacent to the engine clutch, in two rows in a radial direction withinthe interior circumference of the shared clutch drum and configured toselectively transmit the torque of the input shaft to the first andthird output shafts, respectively. The second clutch may be disposed ata rearward side of the input shaft and selectively connecting the inputshaft and the second output shaft.

The connection plate may be formed in a disk shape and disposed betweenthe engine clutch and the first clutch, and the connection platecomprises a radially outer portion spline-engaged with the interiorcircumference of the shared clutch drum, and a radially inner portionspline-engaged with an exterior circumference of the input shaft througha first connecting member.

The engine clutch may include a plurality of engine clutch plates, anengine clutch hub, a plurality of engine clutch disks, and an engineclutch piston. The plurality of engine clutch plates may bespline-engaged with the interior circumference of the shared clutchdrum. The engine clutch hub may be fixed to an extended end of theengine output shaft. The plurality of engine clutch disks may bealternatingly disposed between the plurality of engine clutch plates andspline-engaged with an exterior circumference of the engine clutch hub.The engine clutch piston may be disposed between an engine slavecylinder and the plurality of engine clutch plates to frictionallyoperate the plurality of engine clutch plates and the plurality ofengine clutch disks by the engine slave cylinder.

The engine slave cylinder may be formed at an interior of the supportingend of the front cover.

The first clutch may include a plurality of first clutch plates, a firstclutch hub, a plurality of first clutch disks, and a first clutchpiston. The plurality of first clutch plates may be spline-engaged withthe interior circumference of the shared clutch drum. The first clutchhub may be spline-engaged with an exterior circumference of the firstoutput shaft through a second connecting member. The plurality of firstclutch disks may be alternatingly disposed between the plurality offirst clutch plates and spline-engaged with an exterior circumference ofthe first clutch hub. The first clutch piston may be disposed between afirst slave cylinder and the first clutch plates and configured tofrictionally operate the first clutch plates and the first clutch disksby the first slave cylinder.

The second connecting member may be supported in an axial direction bythe first connecting member via a bearing interposing between the firstand second connecting members.

The third clutch may include a third clutch drum, a plurality of thirdclutch plates, a third clutch hub, a plurality of third clutch disks,and a third clutch piston. The third clutch drum may be disposedradially interior to the first clutch and connected to the shared clutchdrum to be fixed in an axial direction. The plurality of third clutchplates may be spline-engaged with the interior circumference of thethird clutch drum. The third clutch hub may be spline-engaged with anexterior circumference of the third output shaft through a thirdconnecting member. The plurality of third clutch disks may bealternatingly disposed between the plurality of third clutch plates andspline-engaged with an exterior circumference of the third clutch hub.The third clutch piston may be disposed between a third slave cylinderand the third clutch plates and configured to frictionally operate thethird clutch plates and the third clutch disks by the third slavecylinder.

The third connecting member may be supported in an axial direction bythe second connecting member via a bearing interposing between thesecond and third connecting members.

A plurality of return springs may be interposed between the first clutchpiston and the third clutch drum.

The third clutch may further include a restoring unit disposed betweenthe third clutch piston and the third connecting member connected to thethird clutch hub. The restoring unit may include a supporting member anda plurality of springs. The supporting member may have radially innerand outer portions, where the radially inner portion is rotatablysupported by an exterior circumference of the third connecting membervia a bearing and the radially outer portion is spline-engaged with theinterior circumference of the third clutch drum. The plurality ofsprings may be disposed between the supporting member and the thirdclutch piston.

The first and third slave cylinders may be installed in a transmissioncase in two rows in the radial direction.

The second clutch may include a second clutch drum, a plurality ofsecond clutch plates, a second clutch hub, a plurality of second clutchdisks, and a second clutch piston. The second clutch drum may bespline-engaged with the input shaft through a fourth connecting member.The plurality of second clutch plates may be spline-engaged with theinterior circumference of the second clutch drum. The second clutch hubmay be spline-engaged with the second output shaft. The plurality ofsecond clutch disks may be alternatingly disposed between the pluralityof second clutch plates and spline-engaged with an exteriorcircumference of the second clutch hub. The second clutch piston may bedisposed between a second slave cylinder and the second clutch platesand configured to frictionally operate the second clutch plates and thesecond clutch disks by the second slave cylinder.

The fourth connecting member may be supported in an axial direction bythe second output shaft via a bearing interposing between the fourthconnecting member and second output shaft.

The second slave cylinder may be disposed in an end cover fixed to atransmission case.

A plurality of return springs may be interposed between the secondclutch piston and the fourth connecting member.

The second clutch may further include a supporting bearing disposedinside a transmission case so as to act as a reaction plate while thesecond clutch plates and the second clutch disks frictionally cooperate.

According to an exemplary form, a first clutch sharing a shared clutchdrum with the engine clutch is disposed adjacent to the engine clutch ata forward portion of the input shaft, the third clutch is disposed in aradially interior side of the first clutch to form two rows in theradial direction, and the second clutch is separately arranged at arearward portion of the input shaft, thereby reducing number of parts inthe transmission and decreasing length and weight.

In addition, the number of parts for receiving a torque of the motor maybe reduced since the first and third clutches disposed in two rows inthe radial direction share a shared clutch drum with the engine clutch,and the shared clutch drum is formed with a motor gear externallygear-meshed with the motor to receive a torque from the motor.

In addition, since the second clutch is separated to the rearwardportion of the input shaft, there may be provided a better space at aforward portion of the transmission for a differential gear, whichprovides an advantage in the layout of the transmission.

In addition, according to an exemplary form, since the second slavecylinder for operating the second clutch piston is installed inside theend cover, an installation space may be reduced.

Further areas of applicability will become apparent from the descriptionprovided herein. It should be understood that the description andspecific examples are intended for purposes of illustration only and arenot intended to limit the scope of the present disclosure.

DRAWINGS

In order that the disclosure may be well understood, there will now bedescribed various forms thereof, given by way of example, referencebeing made to the accompanying drawings, in which:

FIG. 1 is a cross-sectional view of a power transmission apparatus for ahybrid electric vehicle according to an exemplary form of the presentdisclosure;

FIG. 2 is an enlarged cross-sectional view of a forward portion of apower transmission apparatus for a hybrid electric vehicle according toan exemplary form of the present disclosure; and

FIG. 3 is an enlarged cross-sectional view of a rearward portion of apower transmission apparatus for a hybrid electric vehicle according toan exemplary form of the present disclosure.

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is notintended to limit the present disclosure, application, or uses. Itshould be understood that throughout the drawings, correspondingreference numerals indicate like or corresponding parts and features.

An exemplary form of the present disclosure will hereinafter bedescribed in detail with reference to the accompanying drawings.

In the following description, dividing names of components into first,second and the like is to divide the names because the names of thecomponents are the same as each other and an order thereof is notparticularly limited.

FIG. 1 is a cross-sectional view of a power transmission apparatus for ahybrid electric vehicle according to an exemplary form of the presentdisclosure. FIG. 2 is an enlarged cross-sectional view of a forwardportion of a power transmission apparatus for a hybrid electric vehicleaccording to an exemplary form of the present disclosure. FIG. 3 is anenlarged cross-sectional view of a rearward portion of a powertransmission apparatus for a hybrid electric vehicle according to anexemplary form of the present disclosure.

Referring to FIG. 1 and FIG. 2, a power transmission apparatus for ahybrid electric vehicle according to an exemplary form of the presentdisclosure (hereinafter called a power transmission apparatus) receivestorques from an engine ENG and a motor M, and selectively transmits thereceived torques to an input shaft IS and three output shafts OS1, OS2,and OS3 through four clutches ECL, CL1, CL2, and CL3.

Here, the motor M may include a rotor and a stator and may act as amotor and a generator that generates electricity, as in an electricvehicle.

A power transmission apparatus according to an exemplary form includesan engine output shaft EOS, the input shaft IS, the first, second, andthird output shafts OS1, OS2, and OS3, a shared clutch drum SCD, anengine clutch ECL, and first, second, and third clutches CL1, CL2, andCL3.

The engine output shaft EOS, e.g., a damper output shaft, is a torquemediating shaft receiving the torque of the engine ENG, and is disposedpenetrating supporting end 1 formed at a radially interior side of afront cover FC of a transmission case H.

The input shaft IS is coaxially disposed with engine output shaft EOS inthe transmission case H, and is configured to receive a torque of theengine output shaft EOS by the operation of the engine clutch ECL.

The first output shaft OS1 is formed as a hollow shaft coaxial with theinput shaft and disposed at a forward side of the input shaft IS withoutrotational interference, and the second output shaft OS2 is formed as ahollow shaft coaxial with the input shaft and disposed at a rearwardside of the input shaft IS without rotational interference.

In addition, the third output shaft OS3 is formed as a hollow shaft, andis coaxially disposed with the first output shaft OS1 without rotationalinterference.

The first, second, and third output shafts OS1, OS2, and OS3 areconfigured to receive the torque of the engine output shaft EOS by theoperation of the first, second, and third clutches CL1, CL2, and CL3,while the engine clutch ECL is operated.

That is, the first, second, and third output shafts OS1, OS2, and OS3may selectively receive the torque through the first, second, and thirdclutches CL1, CL2, and CL3, respectively, and the output shaft OS1, OS2,and OS3 are formed with a first output gear G1, a synchronizer SN, athird output gear G3, respectively.

The shared clutch drum SCD is disposed at a forward side of the inputshaft IS. A motor gear MG is formed on an exterior circumference of theshared clutch drum SCD such that the motor M is externally gear-meshedwith the motor gear MG. An interior circumference of the shared clutchdrum SCD is formed in parallel with and rotatably supported, through abearing B, by the supporting end 1 formed at a radially interior side ofthe front cover FC.

In addition, the shared clutch drum SCD is connected to the input shaftIS through a connection plate 3 and a first connecting member 5.

Here, the connection plate 3 is formed in a disk shape and disposedbetween the engine clutch ECL and the first clutch CL1. A radially outerportion of the connection plate 3 is spline-engaged with an interiorcircumference of the shared clutch drum SCD, and a radially innerportion of the connection plate 3 is spline-engaged with an exteriorcircumference of the input shaft IS through the first connecting member5. Therefore, when the engine clutch ECL is operated, the torque of theengine output shaft EOS is transmitted to the input shaft IS.

The connection plate 3 is rotatably supported in an axial direction byan extend end 4 extending rearward from the engine output shaft EOSthrough a bearing B.

The engine clutch ECL shares the shared clutch drum SCD, and isconfigured to selectively transmit a torque between an engine outputshaft EOS and the input shaft IS.

In the engine clutch ECL, a plurality of engine clutch plates 11 and areaction plate 11 a are spline-engaged with the interior circumferenceof the shared clutch drum SCD.

An engine clutch hub 13 is fixed to an extended end 4 of the engineoutput shaft EOS by welding. A plurality of engine clutch disks 15 arealternatingly disposed between the plurality of engine clutch plates 11and the reaction plate 11 a, and are spline-engaged with an exteriorcircumference of the engine clutch hub 13.

An engine clutch piston 17 is disposed to frictionally operate theplurality of engine clutch plates 11 and the plurality of the engineclutch disks 15 along the axial direction by an engine slave cylinderESC.

The engine slave cylinder ESC is formed at an interior of the supportingend 1 of the front cover FC, and the engine clutch piston 17 is disposedbetween the engine slave cylinder ESC and the engine clutch plates 11.

In the engine clutch ECL, a wave spring (not shown) may be installedbetween adjacent engine clutch plates 11 to provide a restoring forceand to maintain a gap between clutch plates 11 and clutch disks 15 in areleased state, thereby reducing or minimizing a drag loss of frictionmembers.

The first and third clutches CL1 and CL3 are disposed, adjacent to theengine clutch ECL, in two rows in the radial direction (i.e., radiallyinward and outward), in a radially interior side of the shared clutchdrum SCD. The first and third clutches CL1 and CL3 are configured toselectively transmit the torque of the input shaft IS to the first andthird output shafts OS1 and OS3, respectively.

The first clutch CL1 shares the shared clutch drum SCD with the engineclutch ECL, and a plurality of first clutch plates 21 are spline-engagedwith the interior circumference of the shared clutch drum SCD.

A first clutch hub 23 is fixed by welding to a second connecting member6 spline-engaged with an exterior circumference of the first outputshaft OS1. A plurality of first clutch disks 25 are alternatinglydisposed between the first clutch plates 21 and spline-engaged with theexterior circumference of the first clutch hub 23.

In addition, a first clutch piston 27 to frictionally operate the firstclutch plates 21 and the first clutch disks 25 is disposed movably inthe axial direction by the first slave cylinder SC1.

The second connecting member 6 is rotatably supported in the axialdirection by the first connecting member 5 via a bearing B interposingbetween the first and second connecting members 5, 6.

The third clutch CL3 is disposed at a radially interior side to thefirst clutch CL1, and a radially outer portion of a third clutch drum 31is connected to the interior circumference of the shared clutch drum SCDto be fixed in the axial direction.

The third clutch drum 31 includes a bent end 31 a that is bent radiallyinward so as to act as a reaction plate of the third clutch 31.

A plurality of third clutch plates 33 are spline-engaged with aninterior circumference of the third clutch drum 31 and are supported inthe axial direction by the bent end 31 a.

A third clutch hub 35 is fixed by welding to a third connecting member 7spline-engaged with an exterior circumference of the third output shaftOS3. A plurality of third clutch disks 37 are alternatingly disposedbetween the third clutch plates 33 and spline-engaged with the exteriorcircumference of the third clutch hub 35.

In addition, a third clutch piston 39 to frictionally operate the thirdclutch plates 33 and the third clutch disks 37 is disposed movably inthe axial direction by a third slave cylinder SC3.

The third connecting member 7 is rotatably supported in the axialdirection by the second connecting member 6 via a bearing B interposingbetween the second and third connecting members 6, 7.

A plurality of return springs SP are disposed along a circumferentialdirection between the first clutch piston 27 of the first clutch CL1 andthe third clutch drum 31 of the third clutch CL3, thereby applying arestoring force to the first clutch piston 27.

The third clutch CL3 further includes a restoring unit 41 between thethird clutch piston 39 and the third connecting member 7 connected tothe third clutch hub 35.

A radially inner portion of the supporting member 43 is rotatablysupported by an exterior circumference of the third connecting member 7via a bearing B interposing between the supporting member and thirdconnecting member, and radially outer portion of the supporting member43 is spline-engaged with the interior circumference of the third clutchdrum 31.

The plurality of springs 45 are disposed between the supporting member43 and the third clutch piston 39 along a circumferential direction,thereby applying a restoring force to the third clutch piston 39.

In the first and third clutches CL1 and CL3, a wave spring (not shown)may be installed between adjacent first clutch plates 21 and adjacentthird clutch plates 33 to provide a restoring force and to maintain agap therebetween in a released state, thereby reducing or minimizing adrag loss of friction members

The first and third slave cylinders SC1 and SC3 may be formed at thetransmission case H, and include cylinder rods to operate the first andthird clutch pistons 27 and 39 of the first and third clutches CL1 andCL3 in the axial direction.

The cylinder rods of the first and third slave cylinders SC1 and SC3rotatably support the first and third clutch pistons 27 and 39 viabearings B, respectively. The present form show a double concentricslave cylinder (double CSC) scheme, where the slave cylinders arearranged in two rows in the radial direction.

Referring to FIG. 3, the second clutch CL2 is disposed at a rearwardside of the input shaft IS, and selectively connects the input shaft ISand the second output shaft OS2.

That is, the second clutch CL2 includes a second clutch drum 51 that isdisposed at the rearward side of the input shaft and is spline-engagedwith an exterior circumference of the input shaft IS through a fourthconnecting member 8.

The fourth connecting member 8 is rotatably supported in the axialdirection by the second output shaft OS2 via a bearing B interposingbetween the fourth connecting member 8 and second output shaft OS2.

A plurality of second clutch plates 53 are spline-engaged with aninterior circumference of the second clutch drum 51.

A radially interior portion of a second clutch hub 55 is spline-engagedwith the second output shaft OS2.

A plurality of second clutch disks 57 are alternatingly disposed betweenthe second clutch plates 53 and spline-engaged with an exteriorcircumference of the second clutch hub 55.

A second clutch piston 59 is disposed between the second slave cylinderSC2 and the second clutch plate 53, and frictionally operates the secondclutch plates 53 and the second clutch disks 57 by the second slavecylinder SC2.

The second slave cylinder SC2 corresponding to the second clutch plate53 is installed in an end cover EC fixed to the transmission case H andcontrols the second clutch piston 59.

Since the second slave cylinder SC2 is installed inside the end coverEC, the second clutch CL2 may be easily assembled, and a sufficientspace may be provided for installation of the second piston clutch 59.

A return spring SP is disposed between the second clutch piston 59 andthe fourth connecting member 8 and applies a restoring force to thesecond clutch piston 59.

The second clutch CL2 further includes a supporting bearing CB disposedon an interior surface of the transmission case H so as to act as areaction plate while the second clutch plates 53 and the second clutchdisks 57 frictionally cooperate.

In addition, a second output gear G2 is disposed on the input shaft ISbetween the first output gear G1 formed at the first output shaft OS1and the synchronizer SN formed at the second output shaft OS2. Thus, thesecond output gear G2 may be synchronously connected to the secondoutput shaft OS2 by the operation of the synchronizer SN.

According to a power transmission apparatus according to an exemplaryform, referring to FIG. 1, when the engine clutch ECL is operated by theengine slave cylinder ESC, the engine clutch disks 15 and the engineclutch plates 11 are frictionally engaged, and the torque of the engineoutput shaft EOS is transmitted to the shared clutch drum SCD throughthe engine clutch hub 13.

The torque transmitted to the shared clutch drum SCD is also transmittedto the input shaft IS through the connection plate 3.

When the first clutch CL1 is operated by the first slave cylinder SC1while the engine clutch ECL is being operated, the first clutch disks 25and the first clutch plates 21 are frictionally engaged, and the torqueof the engine output shaft EOS is transmitted to the first output shaftOS1 through the first clutch hub 23 and the second connecting member 6.

When the third clutch CL3 is operated by the third slave cylinder SC3while the engine clutch ECL is being operated, the third clutch disk 37and the third clutch plate 33 are frictionally engaged, and the torqueof the engine output shaft EOS is transmitted from the third clutch drum31 connected to the shared clutch drum SCD to the third output shaft OS3through the third clutch hub 35 and the third connecting member 7.

When the second clutch CL2 is operated by the second slave cylinder SC2while the engine clutch ECL is being operated, the second clutch disks57 and the second clutch plates 53 are frictionally engaged, and thetorque of the engine output shaft EOS is transmitted to the third outputshaft OS3 sequentially through the connection plate 3 spline-engagedwith the shared clutch drum SCD, the input shaft IS, the fourthconnecting member 8, the second clutch drum 51, and second clutch hub55.

According to an exemplary form as described above, the first clutch CL1sharing the shared clutch drum SCD with the engine clutch ECL isdisposed adjacent to the engine clutch ECL at a forward portion of theinput shaft IS, the third clutch CL3 is disposed in a radially interiorside of the first clutch CL1 to form two rows in the radial direction,and the second clutch CL2 is separately arranged at a rearward portionof the input shaft IS, thereby reducing number of parts crowded forwardin the transmission and decreasing length and weight.

Since the torque of the motor M may be received by the motor gear MGexternally gear-meshed with the motor M, the motor M may be employed inan off-axis scheme where the motor M is provided on an axis separatefrom the input shaft IS, and therefore, the length of a transmissionincluding a torque delivery path of the motor M may be reduced.

In addition, the number of parts for receiving a torque of the motor Mmay be reduced since the first and third clutches CL1 and CL3 disposedin two rows in the radial direction share a shared clutch drum SCD withthe engine clutch ECL, and the shared clutch drum SCD is formed with amotor gear MG externally gear-meshed with the motor M to receive atorque from the motor M.

In addition, since the second clutch CL2 is separated to the rearwardportion of the input shaft IS, there may be provided a better space at aforward portion of the transmission for a differential gear (not shown),which provides an advantage in the layout of the transmission.

In addition, in the second clutch CL2, since the second slave cylinderSC2 for operating the second clutch piston 59 to frictionally operatethe second clutch plates 53 and the second clutch disks 57 is installedin the end cover EC fixed to the transmission case H, the second clutchCL2 may be easily assembled, and a sufficient space may be provided forinstallation of the second piston clutch 59.

While this present disclosure has been described in connection with whatis presently considered to be practical exemplary forms, it is to beunderstood that the present disclosure is not limited to the disclosedforms. On the contrary, it is intended to cover various modificationsand equivalent arrangements included within the spirit and scope of thepresent disclosure.

DESCRIPTION OF SYMBOLS

-   -   FC: front cover    -   H: transmission case    -   EC: end cover    -   1: supporting end    -   3: connection plate    -   4: extended end    -   5, 6, 7, 8: first, second, third, and fourth connecting members    -   IS: input shaft    -   ECL: engine clutch    -   CL1, CL2, CL3: first, second, and third clutches    -   SC1, SC2, SC3: first, second, and third slave cylinders    -   EOS: engine output shaft    -   OS1, OS2, OS3: first, second, third output shafts    -   SCD: shared clutch drum    -   B: bearing    -   CB: supporting bearing    -   11: engine clutch plate    -   13; engine clutch hub    -   15: engine clutch disk    -   17: engine clutch piston    -   21, 53, 33: first, second, and third clutch plates    -   25, 57, 37: first, second, and third clutch disks    -   23, 55, 35: first, second, and third clutch hubs    -   51, 31; second and third clutch drums    -   27, 59, 39: first, second, and third clutch pistons    -   41; restoring unit    -   43: supporting member    -   45: spring

SP: return spring

What is claimed is:
 1. A power transmission apparatus for a hybridelectric vehicle having an engine and a motor as power sources, thepower transmission apparatus comprising: an engine output shaftreceiving a torque of the engine; an input shaft coaxially disposed withthe engine output shaft; first and second output shafts formed as hollowshafts coaxial with the input shaft, and respectively disposed atforward and rearward sides of the input shaft without rotationalinterference; a third output shaft formed as a hollow shaft andcoaxially disposed with the first output shaft without rotationalinterference; a shared clutch drum disposed at the forward side of theinput shaft, and having a motor gear formed on an exterior circumferenceof the shared clutch, wherein the motor is externally gear-meshed withthe motor, and the shared clutch drum has an interior circumferencerotatably supported by a supporting end formed at a radially interiorside of a front cover and is connected to the input shaft through aconnection plate and a first connecting member; an engine clutcharranged on the interior circumference of the shared clutch drum andconfigured to selectively transmit a torque between the engine outputshaft and the input shaft; first and third clutches disposed, adjacentto the engine clutch, in two rows in a radial direction within theinterior circumference of the shared clutch drum and configured toselectively transmit the torque of the input shaft to the first andthird output shafts, respectively; and a second clutch disposed at arearward side of the input shaft and selectively connecting the inputshaft and the second output shaft.
 2. The power transmission apparatusof claim 1, wherein the connection plate is formed in a disk shape anddisposed between the engine clutch and the first clutch, and wherein theconnection plate comprises a radially outer portion spline-engaged withthe interior circumference of the shared clutch drum, and a radiallyinner portion spline-engaged with an exterior circumference of the inputshaft through the first connecting member.
 3. The power transmissionapparatus of claim 1, wherein the engine clutch comprises: a pluralityof engine clutch plates spline-engaged with the interior circumferenceof the shared clutch drum; an engine clutch hub fixed to an extended endof the engine output shaft; a plurality of engine clutch disksalternatingly disposed between the plurality of engine clutch plates andspline-engaged with an exterior circumference of the engine clutch hub;and an engine clutch piston disposed between an engine slave cylinderand the plurality of engine clutch plates to frictionally operate theplurality of engine clutch plates and the plurality of engine clutchdisks by the engine slave cylinder.
 4. The power transmission apparatusof claim 3, wherein the engine slave cylinder is formed at an interiorof the supporting end of the front cover.
 5. The power transmissionapparatus of claim 1, wherein the first clutch comprises: a plurality offirst clutch plates spline-engaged with the interior circumference ofthe shared clutch drum; a first clutch hub spline-engaged with anexterior circumference of the first output shaft through a secondconnecting member; a plurality of first clutch disks alternatinglydisposed between the plurality of first clutch plates and spline-engagedwith an exterior circumference of the first clutch hub; and a firstclutch piston disposed between a first slave cylinder and the pluralityof first clutch plates and configured to frictionally operate theplurality of first clutch plates and the plurality of first clutch disksby the first slave cylinder.
 6. The power transmission apparatus ofclaim 5, wherein the second connecting member is rotatably supported inan axial direction by the first connecting member via a bearinginterposing between the first and second connecting members.
 7. Thepower transmission apparatus of claim 5, wherein the third clutchcomprises: a third clutch drum disposed radially interior to the firstclutch and connected to the shared clutch drum to be fixed in an axialdirection; a plurality of third clutch plates spline-engaged with aninterior circumference of the third clutch drum; a third clutch hubspline-engaged with an exterior circumference of the third output shaftthrough a third connecting member; a plurality of third clutch disksalternatingly disposed between the plurality of third clutch plates andspline-engaged with an exterior circumference of the third clutch hub;and a third clutch piston disposed between a third slave cylinder andthe plurality of third clutch plates and configured to frictionallyoperate the plurality of third clutch plates and the plurality of thirdclutch disks by the third slave cylinder.
 8. The power transmissionapparatus of claim 7, wherein the third connecting member is rotatablysupported in an axial direction by the second connecting member via abearing interposing between the second and third connecting members. 9.The power transmission apparatus of claim 7, wherein a plurality ofreturn springs are interposed between the first clutch piston and thethird clutch drum.
 10. The power transmission apparatus of claim 7,wherein the third clutch further comprises a restoring unit disposedbetween the third clutch piston and the third connecting memberconnected to the third clutch hub.
 11. The power transmission apparatusof claim 10, wherein the restoring unit comprises: a supporting memberhaving radially inner and outer portions, the radially inner portionbeing rotatably supported by an exterior circumference of the thirdconnecting member via a bearing, the radially outer portion beingspline-engaged with the interior circumference of the third clutch drum;and a plurality of springs disposed between the supporting member andthe third clutch piston.
 12. The power transmission apparatus of claim7, wherein the first and third slave cylinders are installed in atransmission case in two rows in the radial direction.
 13. The powertransmission apparatus of claim 1, wherein the second clutch comprises:a second clutch drum spline-engaged with the input shaft through afourth connecting member; a plurality of second clutch platesspline-engaged with an interior circumference of the second clutch drum;a second clutch hub spline-engaged with the second output shaft; aplurality of second clutch disks alternatingly disposed between theplurality of second clutch plates and spline-engaged with an exteriorcircumference of the second clutch hub; and a second clutch pistondisposed between a second slave cylinder and the plurality of secondclutch plates and configured to frictionally operate the plurality ofsecond clutch plates and the plurality of second clutch disks by thesecond slave cylinder.
 14. The power transmission apparatus of claim 13,wherein the fourth connecting member is rotatably supported in an axialdirection by the second output shaft via a bearing interposing betweenthe fourth connecting member and second output shaft.
 15. The powertransmission apparatus of claim 13, wherein the second slave cylinder isdisposed in an end cover fixed to a transmission case.
 16. The powertransmission apparatus of claim 13, wherein a plurality of returnsprings are interposed between the second clutch piston and the fourthconnecting member.
 17. The power transmission apparatus of claim 13,wherein the second clutch further comprises a supporting bearingdisposed inside a transmission case so as to act as a reaction platewhile the plurality of second clutch plates and the plurality of secondclutch disks frictionally cooperate.